1. Field of the Invention
The present invention relates to an electric double layer capacitor and a method of forming the same.
2. Description of the Related Art
In recent years, the electric double layer capacitor has been attractive for further decreases in size and further increases in capacity. For example, the electric double layer capacitor in combination with a lead storage battery has been investigated for a new application to provide driving power to a cell motor of an automobile. The electric double layer capacitor in combination with a solar battery has also been investigated for another new application to provide auxiliary power to a cell motor of an automobile.
The electric double layer capacitor comprises a cell structure which includes a separator, a pair of polarization electrodes, a pair of collectors, a gasket and an electrolytic solution. The separator comprises a porous sheet which is interposed between the paired polarization electrodes. The polarization electrodes have a plate-shape. The paired polarization electrodes sandwiching the separator are interposed between the paired collectors. The collectors have a sheet-shape. The gasket is formed in a frame so that the frame-shaped gasket surrounds a periphery of the layered structure which comprises the separator, the polarization electrodes, and the collectors.
Japanese laid-open patent publication No. 60-144928 discloses that the cell is subjected to an aging process in an atmosphere at a temperature of 70-120xc2x0 C. under application of a voltage for one or a few hours, which voltage level is not higher than an electrolysis voltage of the electrolytic solution and is not lower than a voltage level obtained by a division of a working voltage of the electric double layer capacitor comprising laminations of the cells by the number of the laminations of the cells.
This aging process is carried out in order to identify and remove defective products and stabilize the electrical characteristics of the electric double layer capacitor. The first issue of identifying and removing the defective product will be described. Upon application of a voltage to the cell, a reaction is caused between carbon of an activated carbon and oxygen in the electrolytic solution, wherein the activated carbon forms the polarization electrodes, whereby a carbon dioxide gas or a carbon monoxide gas is generated by this reaction. This generation of the gas increases a gap between the separator and the polarization electrodes. The increase of the gap may increase an equivalent series resistance and allow a leakage of the electrolytic solution. For those reasons, the above loads are intentionally applied to the cell and defective products are withdrawn.
The above described aging process is effective to remove the defective products but does not prevent the production of the defective product nor is it effective to improve the yield.
In the above circumstances, the development of a novel electric double layer capacitor and method of forming the same free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel electric double layer capacitor free from the above problems.
It is a further object of the present invention to provide a novel electric double layer capacitor which is suitable for improvement in the yield.
It is a still further object of the present invention to provide a novel method of forming an electric double layer capacitor free from the above problems.
It is yet a further object of the present invention to provide a novel method of forming an electric double layer capacitor which is suitable for improvement in the yield.
The present invention provides an electrical double layer capacitor including a capacitor cell structure comprising: a separator; polarization electrodes; collectors; and a gasket, wherein at least a part of at least either one of the collectors and the gasket has a gas permeability coefficient of at least 4.0E-12[m3/(m2xc2x7Sxc2x7Pa)].
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.